An estimated 4 to 5 million Americans (about 2% of all ages and 15% of those older than age 65) have some form and degree of cognitive failure. Cognitive failure (dysfunction or loss of cognitive functions, the process by which knowledge is acquired, retained and used) commonly occurs in association with central nervous system (CNS) disorders or conditions, including age-associated memory impairment, delirium (sometimes called acute confusional state), dementia (sometimes classified as Alzheimer's or non-Alzheimer's type), Alzheimer's disease, Parkinson's disease, Huntington's disease (chorea), mental retardation, cerebrovascular disease (e.g., stroke, ischemia), affective disorders (e.g., depression), psychotic disorders (e.g., schizophrenia, autism (Kanner's Syndrome)), neurotic disorders (e.g., anxiety, obsessive-compulsive disorder), attention deficit disorder (ADD), subdural hematoma, normal-pressure hydrocephalus, brain tumor, head or brain trauma.
Cognitive dysfunction is typically manifested by one or more cognitive deficits, which include memory impairment (impaired ability to learn new information or to recall previously learned information), aphasia (language/speech disturbance), apraxia (impaired ability to carry out motor activities despite intact motor function), agnosia (failure to recognize or identify objects despite intact sensory function), disturbance in executive functioning (i.e., planning, organizing, sequencing, abstracting).
Cognitive dysfunction causes significant impairment of social and/or occupational functioning, which can interfere with the ability of an individual to perform activities of daily living and greatly impact the autonomy and quality of life of the individual.
Cognitive training protocols are generally employed in rehabilitating individuals who have some form and degree of cognitive dysfunction. For example, cognitive training protocols are commonly employed in stroke rehabilitation and in age-related memory loss rehabilitation. Because multiple training sessions are often required before an improvement or enhancement of a specific aspect of cognitive performance (ability or function) is obtained in the individuals, cognitive training protocols are often very costly and time-consuming.
Human brain injury often results in motor and cognitive impairments. While advances in critical care medicine and patient management have led to improvements in patient outcome following traumatic brain injury (TBI), there is currently no known treatment to prevent the neuronal cell death and dysfunction that follows TBI. Although multiple treatments have proven neuroprotective in pre-clinical models of TBI, most have failed to show efficacy in humans.
Once a patient is stabilized following TBI, the standard of care dictates extensive motor or cognitive rehabilitation. During this rehabilitation the patient often regains lost skills, finally resulting in improved functional outcome. It would be beneficial if pharmaceutical treatments could be developed to enhance motor or cognitive rehabilitation following TBI, and thus improve functional outcome
In the rat, the well characterized lateral fluid percussion (LFP) brain injury results in extensive apoptotic and necrotic cell death in the hippocampus, thalamus, and cortex (including motor cortex). This neuronal death leads to neuronal dysfunction and impairments in multiple brain systems. Studies have documented deficits in motor and cognitive function (Hamm, R. J. et al., Behav. Brain Res., 59(1-2):169-173 (1993); Gong et al., Brain Res., 700(1-2):299-302 (1995); Hamm, R. J., J. Neurotrauma., 18(11):1207-16 (2001); Floyd et al., J. Neurotrauma., 19(3):303-16 (2002); Hallam et al., J Neurotrauma, 21(5):521-39 (2004)) following LFP brain injury. Extensive rehabilitation can result in improved neurobehavioral outcome following various experimental brain injuries. Current theories hold that during rehabilitation, neurons within the damaged brain tissue and surrounding the damaged area are re-trained to assume some of the lost function. This “re-training” is a form of learning and occurs through the induction of neural plasticity.
Numerous studies have shown that cyclic-AMP (cAMP) and the downstream transcription factor cAMP-responsive element binding protein (CREB) are key regulators in the induction of long-term memory and neural plasticity (Yin, J. C. et al., Cell, 79(1):49-58 (1994); Bourtchuladze, R. et al., Cell, 79(1):59-68 (1994); Impey, S. et al., Nat. Neurosci., 1(7):595-601 (1998)). Genetic or pharmacological interventions which impair cAMP/CREB signaling impair long-term memory formation and synaptic plasticity. Conversely, genetic or pharmacological interventions which enhance cAMP/CREB signaling facilitate long term memory formation and synaptic plasticity.